docs: def validate_manifests(dist, attr, value):
      """Verifies that ``value`` is an expected mapping of package to
      :class:`sassutils.builder.Manifest`.
  
      """
      try:
          Manifest.normalize_manifests(value)
      except TypeError:
          raise distutils.errors.DistutilsSetupError(
              attr + "must be a mapping object like: {'package.name': "
              "sassutils.distutils.Manifest('sass/path')}, or as shorten form: "
              "{'package.name': ('sass/path', 'css/path'}), not " +
              repr(value),
          )